The present invention is directed to a drilling tool, especially a rock drilling tool, for use in a hard material. The drilling tool is formed of an axially extending shaft with a drilling head at one end with the opposite end arranged to fit into the chuck of a drilling device.
For drilling boreholes in hard material, such as concrete, masonry, rock, and the like, drilling tools are used with a drilling head at one end with cutting members of a cutting material, preferably a hard metal. The drilling tools are usually inserted into manually operated drilling devices which, in addition to the rotation of the drilling tool, can also provide axial impacts. Axial impacts are delivered to the chuck end of the drilling tool inserted into a drilling device with the impacts traveling along the shaft and through the drilling head into the material being worked. Accordingly, the material being worked is cut, chiseled and broken down into drilled material. Aside from meeting higher requirements with respect to the advance of the drilling operation and the power required, the drilling tools should also have a service life as long as possible.
From the state of the art, drilling tools are known distinguished by a satisfactory advance of the drilling operation at a justifiable expenditure of power under normal use conditions. The service lives of known drilling tools obtainable under normal conditions of use are acceptable. Such a drilling tool is disclosed in EP-A-0 669 448. This known drilling tool has a shaft with an end to be inserted into the chuck of a manually operated drilling device. Opposite the chuck end, a drilling head is arranged with three cutting surfaces provided on a star-shaped hard metal insert. The cutting surfaces are separated from one another by drilled material removal grooves which feed into discharging grooves for the drilled material with the discharging grooves running helically along the shaft. Such known drilling tool meets the requirements, in particular of a professional user in the case of small and medium sized drill diameters. For drilling tools of larger diameter, however, there is still a certain potential for improvement. In particular, when boreholes are drilled in reinforced concrete, there may be a seizing of the drilling tool when it strikes the reinforcing steel. The danger of seizing increases as the diameter of the drilling head becomes larger.
Therefore, the primary object of the present invention is to provide a drilling tool which overcomes the disadvantages of such tools known in the state of the art. A drilling tool is to be provided, which, independently of the diameter of the drilling head, avoids the danger of the drilling head seizing as it strikes reinforcing steel even when boreholes are drilled into reinforced concrete. In addition, an effective advance of the drilling procedure is obtained with low power consumption and a long service life.
In accordance with the present invention, a drilling tool is gained having the distinguishing features set forth in the claims. The drilling tool of the present invention, in particular a rock drill, includes an axially extending shaft with one end to be inserted into a chuck in a drilling device and the other end firmly secured to a drilling head. The drilling head has at least three hard metal cutting members. At least two adjacent cutting members are located at the circumferential periphery of the drilling head and project radially outwardly from the circumferential periphery and form an angle in the range of about 100 degrees to about 150 degrees with one another. In the circumferential direction, the cutting members are separated from one another by drilled material removal grooves, which, in turn, deliver the drilled material into at least one discharging groove extending helically around the shaft. An enveloping circle about the drilling head is determined by the radial projection of the cutting members outwardly from the drilling head with the circle having a diameter equal to or larger than 15 mm and preferably equal to or larger than 18 mm. The cutting members with the drilled material groove between them are spaced circumferentially apart at an angle of about 100 degrees to about 150 degrees. The circumferential surface of the drilling head has a guiding region and a region containing the drilled material removal grooves with an aperture angle for the grooves having a value of xcex1xe2x89xa6100xe2x88x92e and an axial extent f greater than 0.2e.
Due to the inventive arrangement of the drilled material removal groove located between adjacent cutting members and set at an angle in the range of about 100 degrees to about 150 degrees, the increasing tendency of drilling tools to seize when striking reinforcing steel, encountered in drilling tools with drilled diameters not smaller than 15 mm, and particularly in the case of diameters larger than 32 mm, is counteracted. The drilling head has a guiding surface between the drilled material grooves which is enlarged in the circumferential direction. As a result, additional supporting material remains at the drilling head and its strength is increased. This feature has an advantageous effect on the service life of the drilling tool. Where the cutting members are formed as hard metal inserts, the inserts are secured in the drilling head and are supported by it. As a result, the hard metal inserts are better able to dissipate the transverse forces occurring in operation and to reduce the damage of breakage as well as the danger that the inserts will become detached. Previously, in the case of drilling tools known in the state of the art, it was assumed that as the diameter of the drilling tool increased, the drilling volume removed per unit of time also increased. It has been observed, however, that this is true only up to a certain nominal diameter. It was found that the largest volume of drilled material conveyed with a known drilling tool, especially a drill hammer, is at a nominal diameter of 25 mm. At a nominal diameter of the drilling tool of about 37 mm, the drilled material volume being conveyed decreases once again. In contrast to the existing teachings, according to which the cross section of the drilled material groove or grooves must be increased proportionately with a diameter of the drilling tool, the invention provides the teaching that beyond a limiting diameter of a drilling tool, the cross section of the drilled material grooves increases subproportionately or even remains constant. Due to the inventive construction, optimum discharge of the drilled material is maintained even at larger nominal diameters of the drilling tool. Since the inventive construction is provided especially in an axial section of the drilled material grooves which in the circumferential direction adjoins the axial guiding region at the drilling head extending below the base of the cutting members and extends over the defined minimum region, the tendency of drilling tools with larger diameters to seize upon striking reinforcing steel is counteracted.
For the conveyability of the drilled material grooves having a smaller aperture angle and those in the known state of the art, it proves to be advantageous if two tangents, at the transition from the drilling head circumference to the edges of the drilled material groove, enclose an angle smaller than 45 degrees and preferably in the range of about 15 degrees to 30 degrees.
Accordingly, though the guiding surfaces in the circumferential direction of the drilling head are increased, the drilled material groove formed in accordance with the invention has a sufficiently large cross section for conveying the drilled material produced by the associated cutting member. The drilled material groove is formed with a largest depth having a ratio to the largest width of the drilled material groove that is greater than 0.5, and preferably in the range between 0.6 and 0.9.
For the aperture angle of the drilled material groove located between at least two cutting members disposed at an angle of about 100 degrees to about 150 degrees to one another, a value less than 60 degrees proves to be advantageous.
The drilled material produced by the cutting members must be removed sufficiently quickly from the region of the cutting members and transported out of the borehole through the drilled material grooves and the at least one discharging groove. On the other hand, the drilled material must be comminuted adequately by the cutting members so that the danger of a blockage in the grooves is reduced. Accordingly, it proves to be advantageous for the drilled material grooves to extend essentially axially in the region of the drilling head. Furthermore, drilled material grooves extending essentially axially are also advantageous from the viewpoint of manufacturing technology.
To improve the transport of the drilled material formed by. the cutting members, it is advantageous to have several helical discharging grooves extending around the shaft of the drilling tool. In this way, each drilled material groove directs the drilled material into a separate discharging groove.
In another embodiment of the invention, advantageous relative to the advance of the drilling procedure, the drilling head has three cutting members projecting radially beyond the drilling head""s circumference and separated from one another by drilled material removal grooves.
In a further embodiment of the invention, a drilling head is formed with four cutting members projecting radially beyond the circumference of the drilling head and in each case disposed in pairs at an angle of about 100 degrees to about 150 degrees to one another.
From a manufacturing point of view, it is advantageous if the cutting members are provided by a one piece hard metal insert, constructed star-shaped or X shaped. The hard metal insert is secured in an appropriate recess formed in the face of the drilling head and fastened by soldering.
In still another embodiment of the invention, the drilling head is formed as a whole from hard metal. A hard metal drilling head has the advantage that it can be produced very easily in almost any shape. The mounting of the one piece hard metal drilling head is simplified. In particular, no recesses are formed in the face of the shaft. The drilling head is connected by welding to the drilling tool shaft.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by it use, references should be had to the drawings and description matter in which there are illustrated and described preferred embodiments of the invention.